1. The Field of the Invention
The present invention generally relates to medical devices and methods of use, particularly to pedicle screw systems and methods for their installation.
2. The Relevant Technology
Over the past several decades, spinal surgery has increasingly become an important option available to surgeons and patients in treating issues related to the spine. Because the spine generally provides support and movement for the body, a problem with the spine (e.g., a back disorder) can disrupt even the simplest life activities. In general, thousands of surgical fusions of the spine are performed each year in an attempt to decrease pain and to increase function for the patient. Stabilization of the spine through fusion may be accomplished in a variety of ways, including, for example, the use of pedicle screws, e.g., often used to assist in the fixation of the lumbar and thoracic portions of the spine. Such pedicle screws are generally biocompatible screws that are typically anchored into a vertebra at the pedicle, which is a projection from the body of a given vertebra that connects the body of the vertebra to an arch of the vertebra. Vertebrae generally have two pedicles.
Stability is desired in order to minimize motion while healing occurs, which healing includes fusion of the bone. Pedicle screws have been placed using both traditional open techniques, as well as minimally invasive (e.g., percutaneous) techniques. The placement process itself can be time consuming and difficult. Complexity and difficulty, at least from the perspective of the surgeon, has in some ways been exacerbated by the increased popularity in recent years in the use of minimally invasive techniques for placement of the pedicle screws and associated instrumentation. These techniques generally involve the use of some kind of a percutaneous access device (PAD) which attaches to the pedicle screw, or may be an extension of the screw itself. The PAD allows the surgeon to pass a rod down through the PAD and into the accepting heads of the implanted pedicle screws so that the screws can be connected to each other, forming a composite structure capable of stabilizing that portion of the spine. The connecting rod is generally secured to the pedicle screws by locking nuts which may be inserted through the PADs and tightened. The PADs may eventually be removed.
Many methods have been employed to facilitate delivery and passage of the connecting rod down through a PAD to each respective pedicle screw, although alignment of the connecting rod, so that it is secured to each pedicle screw, has proven to often be a challenge for even the most experienced surgeons. Passing a connecting rod, without direct visualization, through the appropriate receiving head of each successive screw requires precision, patience, and on occasion, a little luck. The reasons for this are that the receiving heads attached to or part of the top of the pedicle screws are typically only slightly larger in diameter than the connecting rod itself. In some cases, clearance between the two is less than a millimeter. As such, even with a rod having a tapered end, proper alignment, insertion, and seating of the rod can be frustrating.
Where only two pedicle screws are to be spanned by the connecting rod, this task may be more readily feasible, as a straight line connects two points. Where three or more pedicle screws are to be spanned by the connecting rod, the process becomes much more difficult, as the three or more screws are rarely on the same line. All too often, one or more of the screws in such an arrangement is enough out of alignment that the surgeon is unable to pass the rod through all of the receiving heads without increasing exposure (i.e., additional incisions) to the surgical site, to provide for direct visualization. It will be apparent that there exists a continuing need for improved methods for delivering such connecting rods, and associated devices used in delivery of the connecting rod.